Strata Committee losing the plot

There’s a lot to unpack here. But @Ziggy you seem to be expecting too much from your building’s strata committee and strata manager (assuming there is one), and from the other owners.
The SC cannot do much, if an owner breaks a Special By-law (whatever that is in your building?). They can issue a Notice to Comply, which they seem to have done. Their next step is to go to the Tribunal to get an Order for that owner to comply, which involves mediation. So you can write to the SC secretary and strata manager, requesting that they do this. They probably can. But it will take months for this to get resolved, so your stress at the SC inactivity, if I’m interpreting the gist of your message correctly, is somewhat unnecessary.
Yes, the SC can authorise the spending of $15k (depending on what state you are living in). The SC IS the owners corporation, and they act as the OC in the day-to-day management of the building. A bathroom waterproofing failure typically costs $30k to fix, so repairs and maintenance can involve this amount of money.
The SC should give notice of their meetings, (depending on the state) but there are ways to do this – which can involved a notice on the building’s notice board 3 days prior to the meeting. But you can access the agenda and minutes of all meetings, and you should do so. It is better to interact with the SC in writing, to the secretary and strata manager, and they can add items you feel are important to the agenda of the next meeting. Note that owners not on the SC have limited rights to speak at meetings, depending on the state you live in – in NSW you can attend SC meetings but cannot speak without the chairman’s permission.
And each state has procedures to filling the roles and positions on the SC when a member resigns or is no longer capable of being a member. Generally, that involves the SC members taking action themselves, and does not involve the wider group of owners.